The first significant adaptive radiation of wife on dry wand occurred during de Devonian, uh-hah-hah-hah. Free-sporing vascuwar pwants began to spread across dry wand, forming extensive forests which covered de continents. By de middwe of de Devonian, severaw groups of pwants had evowved weaves and true roots, and by de end of de period de first seed-bearing pwants appeared. Various terrestriaw ardropods awso became weww-estabwished.

Fish reached substantiaw diversity during dis time, weading de Devonian to often be dubbed de "Age of Fish". The first ray-finned and wobe-finnedbony fish appeared, whiwe de pwacoderms began dominating awmost every known aqwatic environment. The ancestors of aww four-wimbed vertebrates (tetrapods) began adapting to wawking on wand, as deir strong pectoraw and pewvic fins graduawwy evowved into wegs.[10] In de oceans, primitive sharks became more numerous dan in de Siwurian and Late Ordovician.

The rocks of Lummaton Quarry in Torqway in Devon pwayed an earwy rowe in defining de Devonian period.

The period is named after Devon, a county in soudwestern Engwand, where a controversiaw argument in de 1830s over de age and structure of de rocks found distributed droughout de county was eventuawwy resowved by de definition of de Devonian period in de geowogicaw timescawe. The Great Devonian Controversy was a wong period of vigorous argument and counter-argument between de main protagonists of Roderick Murchison wif Adam Sedgwick against Henry De wa Beche supported by George Bewwas Greenough. Murchison and Sedgwick won de debate and named de period dey proposed as de Devonian System.[12][13][14]

In nineteenf-century texts de Devonian has been cawwed de "Owd Red Age", after de red and brown terrestriaw deposits known in de United Kingdom as de Owd Red Sandstone in which earwy fossiw discoveries were found. Anoder common term is "Age of de Fishes",[15] referring to de evowution of severaw major groups of fish dat took pwace during de period. Owder witerature on de Angwo-Wewsh basin divides it into de Downtonian, Dittonian, Breconian and Farwovian stages, de watter dree of which are pwaced in de Devonian, uh-hah-hah-hah.[16]

The Devonian has awso erroneouswy been characterised as a "greenhouse age", due to sampwing bias: most of de earwy Devonian-age discoveries came from de strata of western Europe and eastern Norf America, which at de time straddwed de Eqwator as part of de supercontinent of Euramerica where fossiw signatures of widespread reefs indicate tropicaw cwimates dat were warm and moderatewy humid but in fact de cwimate in de Devonian differed greatwy during its epochs and between geographic regions. For exampwe, during de Earwy Devonian, arid conditions were prevawent drough much of de worwd incwuding Siberia, Austrawia, Norf America, and China, but Africa and Souf America had a warm temperate cwimate. In de Late Devonian, by contrast, arid conditions were wess prevawent across de worwd and temperate cwimates were more common, uh-hah-hah-hah.[citation needed]

The Devonian Period is formawwy broken into Earwy, Middwe and Late subdivisions. The rocks corresponding to dose epochs are referred to as bewonging to de Lower, Middwe and Upper parts of de Devonian System.

Earwy Devonian

The Earwy Devonian wasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began wif de Lochkovian stage, which wasted untiw de Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, and was fowwowed by de Emsian, which wasted untiw de Middwe Devonian began, 393.3± 2.7 miwwion years ago.[citation needed]
During dis time, de first ammonoids appeared, descending from bactritoidnautiwoids. Ammonoids during dis time period were simpwe and differed wittwe from deir nautiwoid counterparts. These ammonoids bewong to de order Agoniatitida, which in water epochs evowved to new ammonoid orders, for exampwe Goniatitida and Cwymeniida. This cwass of cephawopod mowwuscs wouwd dominate de marine fauna untiw de beginning of de Mesozoic era.

Middwe Devonian

The Middwe Devonian comprised two subdivisions: first de Eifewian, which den gave way to de Givetian387.7± 2.7 miwwion years ago.
During dis time de jawwess agnadan fishes began to decwine in diversity in freshwater and marine environments partwy due to drastic environmentaw changes and partwy due to de increasing competition, predation and diversity of jawed fishes. The shawwow, warm, oxygen-depweted waters of Devonian inwand wakes, surrounded by primitive pwants, provided de environment necessary for certain earwy fish to devewop such essentiaw characteristics as weww devewoped wungs, and de abiwity to craww out of de water and onto de wand for short periods of time.[citation needed]

Late Devonian

Finawwy, de Late Devonian started wif de Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which de first forests took shape on wand. The first tetrapods appeared in de fossiw record in de ensuing Famennian subdivision, de beginning and end of which are marked wif extinction events. This wasted untiw de end of de Devonian, 358.9± 2.5 miwwion years ago.[citation needed]

The Devonian was a rewativewy warm period, and probabwy wacked any gwaciers. The temperature gradient from de eqwator to de powes was not as warge as it is today. The weader was awso very arid, mostwy awong de eqwator where it was de driest.[17] Reconstruction of tropicaw sea surface temperature from conodontapatite impwies an average vawue of 30 °C (86 °F) in de Earwy Devonian, uh-hah-hah-hah.[17] CO2 wevews dropped steepwy droughout de Devonian period as de buriaw of de newwy evowved forests drew carbon out of de atmosphere into sediments; dis may be refwected by a Mid-Devonian coowing of around 5 °C (9 °F).[17] The Late Devonian warmed to wevews eqwivawent to de Earwy Devonian; whiwe dere is no corresponding increase in CO2 concentrations, continentaw weadering increases (as predicted by warmer temperatures); furder, a range of evidence, such as pwant distribution, points to a Late Devonian warming.[17] The cwimate wouwd have affected de dominant organisms in reefs; microbes wouwd have been de main reef-forming organisms in warm periods, wif coraws and stromatoporoid sponges taking de dominant rowe in coower times. The warming at de end of de Devonian may even have contributed to de extinction of de stromatoporoids.

The west coast of Devonian Norf America, by contrast, was a passive margin wif deep siwty embayments, river dewtas and estuaries, found today in Idaho and Nevada; an approaching vowcanic iswand arc reached de steep swope of de continentaw shewf in Late Devonian times and began to upwift deep water deposits, a cowwision dat was de prewude to de mountain-buiwding episode at de beginning of de Carboniferous cawwed de Antwer orogeny.[19]

Sea wevews in de Devonian were generawwy high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, de enigmatic hederewwids, microconchids and coraws. Liwy-wike crinoids (animaws, deir resembwance to fwowers notwidstanding) were abundant, and triwobites were stiww fairwy common, uh-hah-hah-hah. Among vertebrates, jawwess armored fish (ostracoderms) decwined in diversity, whiwe de jawed fish (gnadostomes) simuwtaneouswy increased in bof de sea and fresh water. Armored pwacoderms were numerous during de wower stages of de Devonian Period and became extinct in de Late Devonian, perhaps because of competition for food against de oder fish species. Earwy cartiwaginous (Chondrichdyes) and bony fishes (Osteichdyes) awso become diverse and pwayed a warge rowe widin de Devonian seas. The first abundant genus of shark, Cwadosewache, appeared in de oceans during de Devonian Period. The great diversity of fish around at de time has wed to de Devonian being given de name "The Age of Fish" in popuwar cuwture.

The first ammonites awso appeared during or swightwy before de earwy Devonian Period around 400 Mya.[22]

A now dry barrier reef, wocated in present-day Kimberwey Basin of nordwest Austrawia, once extended a dousand kiwometres, fringing a Devonian continent. Reefs in generaw are buiwt by various carbonate-secreting organisms dat have de abiwity to erect wave-resistant frameworks cwose to sea wevew. The main contributors of de Devonian reefs were unwike modern reefs, which are constructed mainwy by coraws and cawcareous awgae. They were composed of cawcareous awgae and coraw-wike stromatoporoids, and tabuwate and rugose coraws, in dat order of importance.[cwarification needed]

Dunkweosteus, one of de wargest armoured fish ever to roam de pwanet, wived during de wate Devonian

By de Devonian Period, wife was weww underway in its cowonisation of de wand. The moss forests and bacteriaw and awgaw mats of de Siwurian were joined earwy in de period by primitive rooted pwants dat created de first stabwe soiws and harbored ardropods wike mites, scorpions, trigonotarbids[23] and myriapods (awdough ardropods appeared on wand much earwier dan in de Earwy Devonian[24] and de existence of fossiws such as Cwimactichnites suggest dat wand ardropods may have appeared as earwy as de Cambrian). Awso de first possibwe fossiws of insects appeared around 416 Mya in de Earwy Devonian, uh-hah-hah-hah. Evidence for de earwiest tetrapods takes de form of trace fossiws in shawwow wagoon environments widin a marine carbonate pwatform/shewf during de Middwe Devonian,[25] awdough dese traces have been qwestioned and an interpretation as fish feeding traces (Piscichnus) has been advanced.[26]

The Devonian period marks de beginning of extensive wand cowonisation by pwants. Wif warge wand-dwewwing herbivores not yet present, warge forests grew and shaped de wandscape.

Many Earwy Devonian pwants did not have true roots or weaves wike extant pwants awdough vascuwar tissue is observed in many of dose pwants. Some of de earwy wand pwants such as Drepanophycus wikewy spread by vegetative growf and spores.[27] The earwiest wand pwants such as Cooksonia consisted of weafwess, dichotomous axes and terminaw sporangia and were generawwy very short-statured, and grew hardwy more dan a few centimetres taww.[28] By far de wargest wand organism during dis period was de enigmatic Prototaxites, which was possibwy de fruiting body of an enormous fungus,[29] rowwed wiverwort mat,[30] or anoder organism of uncertain affinities[31] dat stood more dan 8 metres taww, and towered over de wow, carpet-wike vegetation, uh-hah-hah-hah. By de Middwe Devonian, shrub-wike forests of primitive pwants existed: wycophytes, horsetaiws, ferns, and progymnosperms had evowved. Most of dese pwants had true roots and weaves, and many were qwite taww. The earwiest-known trees, from de genus Wattieza, appeared in de Late Devonian around 385 Mya.[32] In de Late Devonian, de tree-wike ancestraw Progymnosperm Archaeopteris which had conifer-wike true wood and fern-wike fowiage and de cwadoxywopsids grew.[33] (See awso: wignin.) These are de owdest-known trees of de worwd's first forests. By de end of de Devonian, de first seed-forming pwants had appeared. This rapid appearance of so many pwant groups and growf forms has been cawwed de "Devonian Expwosion".

Primitive ardropods co-evowved wif dis diversified terrestriaw vegetation structure. The evowving co-dependence of insects and seed-pwants dat characterised a recognisabwy modern worwd had its genesis in de Late Devonian period. The devewopment of soiws and pwant root systems probabwy wed to changes in de speed and pattern of erosion and sediment deposition, uh-hah-hah-hah. The rapid evowution of a terrestriaw ecosystem dat contained copious animaws opened de way for de first vertebrates to seek out a terrestriaw wiving. By de end of de Devonian, ardropods were sowidwy estabwished on de wand.[34]

The Late Devonian is characterised by dree episodes of extinction ("Late D")

A major extinction occurred at de beginning of de wast phase of de Devonian period, de Famennian faunaw stage (de Frasnian-Famennian boundary), about 372.2 Mya, when aww de fossiw agnadan fishes, save for de psammosteidheterostraci, suddenwy disappeared. A second strong puwse cwosed de Devonian period. The Late Devonian extinction was one of five major extinction events in de history of de Earf's biota, and was more drastic dan de famiwiar extinction event dat cwosed de Cretaceous.

The Devonian extinction crisis primariwy affected de marine community, and sewectivewy affected shawwow warm-water organisms rader dan coow-water organisms. The most important group to be affected by dis extinction event were de reef-buiwders of de great Devonian reef systems.

Amongst de severewy affected marine groups were de brachiopods, triwobites, ammonites, conodonts, and acritarchs, as weww as jawwess fish, and aww pwacoderms. Land pwants as weww as freshwater species, such as our tetrapod ancestors, were rewativewy unaffected by de Late Devonian extinction event (dere is a counterargument dat de Devonian extinctions nearwy wiped out de tetrapods[35]).

The reasons for de Late Devonian extinctions are stiww unknown, and aww expwanations remain specuwative.[36]CanadianpaweontowogistDigby McLaren suggested in 1969 dat de Devonian extinction events were caused by an asteroid impact. However, whiwe dere were Late Devonian cowwision events (see de Awamo bowide impact), wittwe evidence supports de existence of a warge enough Devonian crater.

Sedgwick and Murchison coined de term "Devonian system" in: Adam Sedgwick and Roderick Impey Murchison (1840) "On de physicaw structure of Devonshire, and on de subdivisions and geowogicaw rewations of its owder stratified deposits, etc.," Transactions of de Geowogicaw Society of London, 2nd series, 5 (part II) : 633-687 (Part I) and 688-705 (Part II). From p. 701: "We propose derefore, for de future, to designate dese groups cowwectivewy by de name Devonian system, … ."

Sedgwick and Murchison acknowwedged Wiwwiam Lonsdawe's rowe in proposing, on de basis of fossiw evidence, de existence of a Devonian stratum between dose of de Siwurian and Carboniferous periods. From (Sedgwick and Murchison, 1840), p. 690: "Again, Mr. Lonsdawe, after an extensive examination of de fossiws of Souf Devon, had pronounced dem, more dan a year since, to form a group intermediate between dose of de Carboniferous and Siwurian systems, … ."

Wiwwiam Lonsdawe stated dat in December 1837 he had suggested de existence of a stratum between de Siwurian and Carboniferous ones. See: Wiwwiam Lonsdawe (1840) "Notes on de age of wimestones from souf Devonshire,"Transactions of de Geowogicaw Society of London, 2nd series, 5 (part II) : 721-738 ; see especiawwy pp. 724 and 727. From p. 724: " … Mr. Austen's communication [was] read December 1837, … . It was immediatewy after de reading of dat paper … dat I formed de opinion rewative to de wimestones of Devonshire being of de age of de owd red sandstone; and which I afterwards suggested first to Mr. Murchison and den to Prof. Sedgwick, … ."